Spatial organization of calcium dynamics in growth cones of sensory neurones

The concentration of calcium ions in the cytosol ([Ca2+](i)) has a dominant influence on neuronal development. A [Ca2+](i) rise can, depending on the amplitude and location, promote outgrowth or dramatically inhibit it. We have used the fluorescent calcium indicators Fura-2 and Fura-2 dextran to measure [Ca2+](i) dynamics in sensory neurones from the adult rat. [Ca2+](i) was low and uniform in advancing growth cones, even during specific behaviours such as protrusion, filling and consolidation. A brief train of action potentials caused [Ca2+](i) to rise at the extreme leading edge of the growth cone. [Ca2+](i) changes in more proximal regions of the growth cone were much smaller. This spatially organized [Ca2+](i) change, which may result from a concentration of calcium channels at the growth cone leading edge, is likely to function in spontaneously active regenerating axons in vivo to specifically activate calcium-dependent processes at the growth cone tip.